The present invention relates to the field of waste water treatment, and provides a system and method for oxygenating waste water at an early stage of the waste water treatment process.
In a typical waste water treatment facility, waste water is collected from various sources, including residential and/or industrial sources. The waste water from these sources is initially held in a collection basin, also known as a diversion box. The water is then conveyed to one or more settling tanks, wherein debris in the water is allowed to settle. The water can then be filtered one or more times, aerated, and treated with chemicals such as ozone, chlorine, etc. There may be one or more further collection basins positioned before the first filtration stage.
Bacteria in the water attack organic material in the water, consuming oxygen in the process. But since the water reaching the collection basin is delivered through underground conduits, the supply of oxygen in the water is limited. If there is insufficient oxygen available to support the reactions which would naturally occur in the presence of oxygen, anaerobic reactions take place instead. Such reactions typically include the chemical combination of sulfur with hydrogen to produce hydrogen sulfide, a very odorous gas. Elimination of foul odors, and promoting biological oxidation reactions, are major concerns in the field of waste water treatment.
The known solution to the above-described problem is to oxygenate the water. When the deficiency of dissolved oxygen is overcome, the odor problem is greatly reduced or eliminated.
It has therefore been proposed, in the prior art, to provide a source of pure oxygen at high pressure, to dissolve this oxygen in a sample of the waste water, and to return the oxygenated sample to the basin being treated.
One prior art arrangement for performing the above steps is shown in FIG. 1. Oxygen from a supply (not shown) flows into conduit 1, through valve 3, and into mixing device 5. Waste water located in collection basin 7 is drawn out by pump 11, through suction pipe 9, and sent to the mixing device. The mixture of oxygen and waste water is then introduced into the collection basin through discharge pipe 13. The discharge pipe is connected to a plurality of nozzles 15 located at or near the bottom of the collection basin.
The major problem with the method described above is that the nozzles easily become clogged with debris which is almost always present in the waste water.
Another proposed solution of the prior art is shown in FIG. 2. In this embodiment, the nozzles have been eliminated. Instead, the ends of discharge pipe 21 and suction pipe 23 are displaced from the bottom of the basin. In the example given in the figure, these ends are positioned about midway between the top and bottom of the basin. In this embodiment there are two oxygen lines, one of which is used as a backup in the event that the pump 27 becomes clogged or in the event that cavitation renders the pump ineffective. Also in this embodiment, a screen (not shown) is used at the inlet to suction pipe 23, to prevent debris in the water from interfering with the operation of pump 27.
The system described above is still not practical. Its major problem is that it causes cavitation in the pump. As the screen becomes clogged, the pump has less and less to pull, resulting in reduced suction in the line. Changes in pressure in the line may cause oxygen to come out of solution, and if this occurs, the pump will tend to pull both gas and water out of the basin. The presence of gas in the line causes damage to the pump.
The present invention provides a system and method which allows the oxygenation of waste water in a collection basin, but which nevertheless does not suffer from the disadvantages of the prior art described above.
The present invention comprises a system which connects a source of pressurized oxygen to a mixing device. A pump draws some of the waste water out of a collection basin, and directs this water to the mixing device, where the water and oxygen are mixed so that the oxygen is dissolved in the water. This oxygen-enriched water produced in the mixing device is conveyed to a discharge pipe, the end of which sits within the waste water in the basin. A suction pipe, connected to the pump, withdraws a portion of the contents of the basin. The ends of the discharge pipe and the suction pipe are at different vertical levels. In the preferred embodiment, the end of the discharge pipe is located above the end of the suction pipe. In operation, water is continuously withdrawn from the basin, while oxygen-enriched water is continuously injected into the basin.
The end of the discharge pipe preferably includes a blind flange, which tends to prevent returned waste water from flowing directly out of the discharge pipe. Instead, the oxygen-water mixture is directed out of the discharge pipe, through holes in its side wall, in a direction which is non-parallel to the longitudinal axis of the pipe. This arrangement assures that the mixture will not directly enter the suction pipe, but will instead become evenly dispersed through the basin. Thus, the suction pipe does not xe2x80x9cshort-circuitxe2x80x9d the discharge pipe.
The invention therefore also includes the method of oxygenating the contents of a waste water collection basin by mixing some of the waste water with oxygen, such that the oxygen becomes dissolved in the water, and introducing the oxygen-enriched water into the basin at a vertical level different from that at which water in the basin is removed. The introducing step is performed by introducing the mixture in a direction which is generally perpendicular, or at least non-parallel, to the flow of fluid in the discharge pipe.
The present invention virtually eliminates the cavitation problem associated with systems of the prior art, making it feasible to oxygenate waste water at an early stage of its processing.
The present invention therefore has the primary object of providing a system and method for oxygenation of waste water.
The invention has the further object of preventing cavitation in a pump used to draw waste water from a collection basin, for use in an oxygenation process.
The invention has the further object of reducing or eliminating foul odors in a collection basin in a waste water treatment facility.
The invention has the further object of oxygenating waste water at a relatively early stage in a waste water treatment plant.
The invention has the further object of improving the efficiency and effectiveness of waste water treatment.
The reader skilled in the art will recognize other objects and advantages of the present invention, from a reading of the following brief description of the drawings, the detailed description of the invention, and the appended claims.